The invention concerns a process for the treatment of wastes, involving a first mixture of solid and liquid waste materials, which contains at least one metal such as Fe and/or compounds thereof, for example oxides, in such a condition that it cannot be used or can be used only with difficulty.
It is known for waste materials to be subjected to treatment, the aim of which is to put them into a condition in which they can be handled. Thus for example DE 32 08 699 C2 discloses a process for the production of granulated copperas--FeSO.sub.4.7H.sub.2 O. The latter is a waste product which is produced primarily in the manufacture of titanium dioxide. With pH-values of between 1 and 2, it is highly acid. It has a tendency to cake together so that it can only be removed from storage containers with considerable difficulty. The procedure involves mixing copperas with dried brown coal or lignite in dust form, in such an amount that the resulting mixture is capable of a trickle flow. Copperas is a relatively homogeneous waste material. That procedure is expensive as brown coal or lignite dust which may have only a low water content represents an expensive material. DE 32 15 727 Al discloses a process for the treatment of red mud which is a waste product that is produced in the production of aluminium in the form of iron oxide (Fe.sub.2 O.sub.3, Fe .sub.3 O.sub.4), being present in the form of an alkaline aqueous suspension. That suspension is filtered, with the red mud being deposited on the filter cloth. That procedure provides that the red mud is mixed with coal dust, more especially brown coal or lignite dust, in order to produce a mixture which is capable of trickle flow. That procedure is also expensive, especially as comparatively large amounts of coal dust must be used in order to produce the desired effect of a mixture which is capable of trickle flow. Red mud however is also a comparatively homogeneous waste product.
Many areas of industry involve the production of waste products which are substantially less homogeneous, as they frequently represent a mixture consisting of a plurality of solid and liquid components. A typical product of that kind is rolling scale slurry or sludge. Rolling scale is for example the oxidation layers which are produced when rolling and forging steel and when drawing wire. In the rolling mill, the rolling scale is swept off the rolled surface of the metal during the rolling operation, for example by means of a jet of water. The waste water which is charged with fine-grain rolling scale collects beneath the roll stand in the scale pit in which the roll scale slurry is deposited; the roll scale slurry, besides the metal oxide and water, also contains impurities due to carbon-bearing lubricants and all possible objects and articles which are thrown away in operation of the rolling mill. At any event, as regards the finer-grain constituents of the rolling scale slurry or sludge, the latter is extremely difficult to handle so that in general it is not re-used, although its high content of iron oxide means that it would represent a valuable starting material. However, recycling for example to a metallurgical procedure would also involve taking account of the content of lubricant materials. Thus rolling scale slurry may contain for example more than 5% lubricating oil or the like so that it is not normally possible to treat the rolling scale slurry for example by sintering, as the combustion products which result from the oil components in the sintering operation give rise to problems.
Other waste materials which give rise to difficulties in regard to re-use thereof are sludges which originate from the production of iron oxide for the manufacture of ink or dye pigments, and black sludge which is produced in the manufacture of aluminum and which essentially comprises Al.sub.2 O.sub.3, carbon predominantly in the form of graphite and between 35 and 40% water. The re-use of blast furnace flue gas dusts, blast furnace flue gas slurries or sludges, sinter dusts, converter dusts, converter sludges and foundry dusts which are produced in metallurgical works, as well as grinding dusts, grinding slurries and sludges, and dusts and sludges originating from cutting machining operations, also give rise to difficulties as they frequently occur in the form of a mixture which is difficult to handle or which also cannot be directly re-used.
Difficulties in terms of handling further arise by virtue of the fact that the above-indicated waste materials and waste mixtures occur in very different compositions and thus involve different consistencies. The mixtures are frequently also highly heterogeneous, for example due to the foreign objects which are contained in rolling scale sludge and which may also involve small pieces of waste from the rolled material; the fact that the mixtures are highly heterogeneous also makes it difficult to subject them to suitable treatment steps to produce a handleable product which can be re-used.